1. Field of the Invention
This invention relates to a reproducing apparatus and more particularly to a reproduction equalizing process for a digital signal reproduced from a recording medium.
2. Description of the Related Art
In transmitting signals, it has generally been practiced to carry out an equalizing process, on the signal receiving side, to compensate in any loss for obtaining good signals by controlling the frequency characteristic of signals received from a transmission system.
Known transmitting apparatuses of the kind mentioned above include, for example, a digital VTR which records and reproduces a video signal (in the form of a digital signal) on and from a magnetic tape and is also arranged to perform an equalizing process on reproduced signals.
A magnetic recording/reproducing apparatus such as the digital VTR has a transmission characteristic such that the signal transmitted deteriorates in low and high frequency domains. The deterioration in the low frequency domain is attributable to a differential characteristic which is intrinsic to an induction coil type magnetic head and also a low-band cutoff characteristic of a rotary transformer. The deterioration in the high frequency domain is caused by a loss resulting from the wavelength dependency of the recording medium, a core loss of the magnetic head, and a spacing loss between the magnetic head and the recording medium.
In the case of the digital VTR or a digital data recorder, if the deterioration of such characteristics is excessive, there arises some waveform distortion such as intersymbol interference or the like, which greatly deteriorates the transmission characteristic.
In view of the above, digital VTRs have been arranged to use a waveform equalizing circuit to make the reproduced signal have an adequate waveform by compensating for signal deterioration resulting from the above-stated factors. FIG. 1 shows in a block diagram the arrangement of the conventional digital VTR.
Referring to FIG. 1, a signal reproduced from a tape T by a head 1 is supplied via a rotary transformer 2 to a preamplifier 3 to be amplified therein. The amplified reproduced signal is supplied to an integrating circuit 4. The integrating circuit 4 processes the signal to compensate mainly for deterioration of the low frequency domain of the signal. The signal thus compensated is supplied to an amplitude equalizer 5 to be compensated for deterioration of the high frequency domain. The signal is then supplied to a phase equalizer 6.
The phase equalizer 6 processes the signal from the amplitude equalizer 5 to compensate for a phase deviation of a whole circuit resulting from magnetic recording and reproducing characteristics and the characteristic of the circuit. A signal 7 is thus obtained as an output of the phase equalizer 6. The signal 7 is supplied to a circuit of a subsequent stage. The circuit of the subsequent stage then restores the signal 7 to its original state of digital data.
Generally, the frequency characteristic of each of the integrating circuit 4, the amplitude equalizer 5 and the phase equalizer 6 is arranged to be controllable. A desired frequency characteristic can be obtained by adjusting a plurality of control points within each of these circuits according to the state of the reproduced signal and the kind of the magnetic tape in use.
In the case of the VTR of the above-stated kind, however, it is hardly possible to adequately adjust the frequency characteristic of the integrating circuit and those of the equalizers since the plurality of adjusting points are affected by each other. In other words, in individually adjusting the plurality of adjusting parts for each of these circuits, after the frequency characteristic is controlled and adjusted to an optimum characteristic for one adjusting part, the characteristic of this part would be affected by the adjustment made for another adjusting part, thereby necessitating readjustment.
Therefore, according to the arrangement of the conventional digital VTR, the frequency characteristic either cannot be adjusted as desired or necessitates much time and labor for adjustment.
This invention is directed to the solution of the problem of the prior art mentioned above.
It is, therefore, an object of this invention to provide an apparatus which is arranged to be capable of obtaining an optimum equalizing characteristic through a simple control.
To attain this object, a reproducing apparatus arranged according to this invention is provided with reproducing means for reproducing a signal, equalizing means, having a plurality of controllable elements, for equalizing the signal reproduced by the reproducing means, and control means for controlling an equalizing characteristic of the equalizing means by controlling, with a single parameter, the plurality of controllable elements of the equalizing means.
It is another object of this invention to provide an apparatus arranged to control and optimize characteristics of circuits resulting from a resonance frequency and a quality factor (Q).